The present invention relates to a method for measuring the values of parameters relating to an electrically conductive material in solid or liquid form, such as the distance of an electrically conductive material from a given point, linear dimensions of a body incorporating the conductive material, the temperature of the material, or its electrical conductivity; and in which method an electromagnetic field is caused to penetrate the electrically conductive material at least partially. The invention also relates to a measuring system for carrying out the method.
The electrically conductive material should be at least substantially non-magnetic, for instance a metal billet or bloom in the process of being rolled, a metal rod during a drawing operation, a machined metal product during the process of inspecting the object and making material checks, a cast metal ingot in a continuous casting process, or a metal bath during a treatment process. The electrically conductive material is not limited to metals, but may comprise other materials of good electrical conductivity, such as graphite or a metal compound heated to a high temperature.
It is previously known to utilize a magnetic field for measuring the values of magnitudes of parametric values of the aforesaid kind in conjunction with electrically conductive materials. In this regard it is conventional practice to generate a sinusoidal alternating magnetic field in the close proximity of the electrically conductive material and to sense the influence of the material on the magnetic field, in the form of an induced change either in the coil which generates the magnetic field or in one or more separate sensing coils. When only one coil is used, there is detected or sensed the amplitude and/or the changes in phase across the coil. This means, however, that the change will be small in relation to the applied field or voltage, and hence it is difficult to obtain accurate measurements. Furthermore, with this kind of measuring process it is very difficult to differentiate between the influences exerted by variations in two or more mutually different parameters. The use of one or more separate sensing coils will, to a certain extent, overcome the problem that the change induced constitutes only a small part of the fundamental signal. However, the geometrical arrangement of the coils presents a problem which often results in inaccurate sensing. Furthermore, the difficulty experienced in differentiating between the influence exerted by variations of two parameters at one and the same time is also encountered in this case, while it is impossible to differentiate between variations of three parameters at the same time, since only two measurement parameters, phase and amplitude, can be measured.
Also described in the literature are coil arrangements which generate a sinusoidal field in accordance with the aforegoing and which are geometrically formed in a particular manner so as to obtain increased sensitivity or response to one magnitude and decreased sensitivity or response to the other. This provides for some degree of demarcation between the different parameters, but the arrangements are complicated and are sensitive to variations in geometry.
Powerful direct-current magnetic fields have previously been used in conjunction with measuring the magnetic properties of an electrically conductive material. The purpose of this powerful d.c. magnetic field is to change the magnetic properties of the material, i.e. to magnetize and demagnetize the object to be measured. Consequently, the method will not function with non-magnetic materials.
The Swedish Patent Applications 76057603, 7605759, 7605761 and 77104818 teach systems and coil configurations for electro-magnetically measuring parameters according to the above in conjunction with liquid, electrically conductive materials heated to high temperatures. Although the measuring systems described in these documents have been found to function well in practice, there remains a large number of applications or fields in which the demands on accuracy and the possibility of measuring a number of varying parameters independently of one another are not satisfied.